1. Field of Invention
This invention relates to camouflaging means and a method for disguising the visible and infrared image of military targets which may be substantially warmer than their surroundings by having been exposed to the sun, or in which heat may be produced by internal combustion engines, electric motors, generators, or transformers.
2. Description of Prior Art
Camouflage materials providing protection in the visible spectral region (wavelength from 400-700 millimicrons) by color adaptation to the background are well known to the art. However, most currently used camouflage paints, irrespective of their color in the visible spectral region, tend to have high emissivities in the infrared spectral regions from 3 to 5 and from 8 to 14 microns. (No significant infrared radiation is propagated over long distances outside these two "windows" because of absorption by water vapor and carbon dioxide contained in the atmosphere.)
The emissivities of such paints tend, on average, to be significantly higher than those of most naturally occurring backgrounds. Therefore, targets painted with such paints can be clearly detected by imaging devices operating in the infrared spectral ranges. Moreover, many such targets have heat sources such as internal combustion engines, electric generators and motors which create a temperature contrast with the natural background which further enhance the detectability of such targets by means of infrared sensing devices. To provide protection against sensing devices operating in the infrared spectral regions, camouflaging materials with controlled electromagnetic emissivities in the infrared regions as well as in the near-by radar region have been proposed.
U.S. Pat. Nos. 4,560,595 and 4,615,921 provide a thin metallic randomly deformed camouflage layer covered by two different plastic materials having different emissivities in the infrared region, simulating the surrounding terrain. U.S. Pat. No. 4,495,239 provides camouflage nets and thermal insulation mats using pigments for the visible and near infrared spectral region, and a binder with high transparency to radiation in the infrared range, providing low emissivity in that range, as well as in the radar range from 3 to 3000 GHz. U.S. Pat. No. 4,142,015 provides a layer of insulating foamed plastic, applied to the surface of the target to be camouflaged, that varies randomly to blur the visual and thermal image of the target. U.S. Pat. No. 2,294,675 provides a coating composition having a dark color in the visible spectral range and a low emissivity in the infrared range.
The methods and apparatus provided heretofore for disguising military targets both in the visible and infrared spectral ranges suffer from the drawback that the effective emissivity of the camouflage material in the infrared ranges cannot readily be closely adapted to that of the surroundings from which the target should be indistinguishable when viewed by infrared detection equipment. Moreover, the thermal "signature" of such targets resulting from internal heat sources such as internal combustion engines, exhaust pipes, electric motors or generators, or transformers, cannot readily be disguised by known methods.
The object of present invention therefore is to provide means and a method for structuring the camouflaging surface in such manner that there is both color adaptation in the visual range and an effective emissivity in the infrared range which can be designed to simulate that of virtually any natural background, and which can furthermore be designed to disguise hot regions of the target which would ordinarily be clearly discernible with infrared detection devices.